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Q: We're soon plastering our strawbale home in North Dakota. We'd like to use ferrous sulfate to stain/color the exterior. Should we mix this in with the finish (color) coat, or try to "paint" on a solution afterwards? We're using a cement-based plaster for the exterior. A: As far as I know you can only apply the ferrous sulphate to the stucco when it is "green". I do not know of anyone adding it within the mix. Even is you could, it would use a lot more Ferrous Sulphate and it is easy to brush on afterward. You want to apply the Ferrous Sulphate while the walls are still moist and you want to make sure you saturate the cement stucco. It will turn green at first, but will turn into the lovely rust color later, and continue to deepen over a few months time. You may want to apply 2-3 coats waiting a day in between each one. You may apply this with a roller. Q: I'm looking for information on using pumice in stucco mix. I know that thin layers of pumice crete are brittle. Can this be overcome by using pumice with sand and lime? If so, it might also solve the problem of breathability with strawbale walls. I am interested in mixing a lighter scratch coat to create less strain on the walls. A: (Kelly) I don't have any direct experience mixing pumice with other ingredients for plastering, but I know that it has been done successfully. In fact it is recommended to combine such pozzolan material as pumice with lime to make it set up firmer and be more durable. I would say that your lime/sand/pumice mix would make an excellent plaster, and suggest that you do some trial mixes to see which results you like. This would definitely produce a more breathable plaster than ordinary cement stucco. Q: My husband and I live in Southern California and plan to remodel our home by turning it into a 'green home' as well as adding a second story. Although I've done a lot of research thus far (i.e., natural flooring, natural interior walls), I am stuck on a few materials. Number 1: Exterior Walls. I would like to have whatever is the equivalent to 'natural stucco'. What are our natural/non-toxic choices? If it's a lime-wash, are there any natural pigments in order to have color? A: Yes, the most likely natural exterior wall finish to mimic stucco is Lime plaster. However, this application would depend on a great many things. It is important to know what kind of wall system it is going on top of. If you are living in a house with a natural wall system eg., straw bales, adobe etc., it is fairly simple for someone that understands plaster (although the application of lime plaster should be done by a lime professional). If you are trying to do this on top of a stick frame wall system it is more complex, and would need some serious consideration. Random things to know: -The sub-surface the lime would adhere to would need to be stable to prevent cracks in the lime. -The lime would need some kind of rough surface to adhere to. -Lime is calcium carbonate and turns itself back into limestone through a process of taking carbon dioxide out of the atmosphere. This process of the plaster hardening is slower (unlike cement) and needs moisture to carry out this function. I mention this as you are in a warm dry climate. I would suggest that if you choose to do lime, it should be done when there is cloud cover and moisture available either naturally or created by you and/or your contract person (this needs to happen for several weeks for the lime to be hard). If it is applied under inappropriate conditions the lime plaster will be weak. Regarding color. There are pigments that can be added to lime plaster or lime wash. You can choose any colors that are alkali fast. Lime is an alkali substance and will bleach out anything else. Research places in your area that carry pigments. I purchase pigments from building supply stores, dry wall suppliers, and certain shops that cater to restoration work and fine artists. The latter usually have staff that are well versed in which pigments are lime-compatible and even have them coded. I know that you can buy pigments via mail order from a shop in San Fransisco named Sinopia. They are very knowledgeable. Their contact information is: Sinopia 415 824 3180 www.sinopia.com . Q: What are the advantages of using an earth clay interior finish plaster, like "American clay" over say gypsum or lime?? A: The advantage of using an earthen plaster over lime or gypsum plasters are chiefly related to the ease of application and skill level. Earthen plasters are easy to use because they give you a longer working time. Earthen plasters are "drying" not "setting". They are not undergoing a chemical reaction as gypsum and lime are. Gypsum plasters have a shorter working time and can harden very quickly depending upon which gypsum plaster you are using (in some cases the working time is 20 minutes). Although lime sets much more slowly than gypsum, it requires a careful method of application. If you overwork a lime plaster during application it may result in cracking. Earthen plasters are safe to use. You may apply earthen plasters with your bare hands. Lime is an alkaline substance and therefore, caustic. You need to wear gloves, long sleeves, and eye protection to avoid the possibility of lime burns. Earthen plasters offer a particular range in color that are often deeper and warmer than gypsum or lime. Lime and gypsum are white materials that can be altered by adding pigments. However, any color added to white will result in a pastel color when mixed with the lime or gypsum. Pigments may also be added to the clay plasters but you may achieve a deeper darker tone as the earth colors (clays) can range from white to dark browns. In addition, lime plasters are limited to lime compatible pigments due to their alkalinity. Q: My father and I are building a home in Flagstaff. We've decided to use Ecrete and natural clay as our finish. I need to know price on labor and approximately how many men you need on a plastering crew. Q: Do you use zeolite at all in your construction projects? A: I do not use zeolite in any of my construction processes. My natural building projects are much more basic. I use raw materials such as: earth, straw, aggregates, minerals such as lime and gypsum, and the like. I do not know anyone using zeolite within the natural building community. Possibly someone working with pozzolanic plasters since zeolite is likely to occur within those materials. A: I haven't done much work mixing lime with soil. I know there must be a lot of people out there that have. I put the word out in the natural building community and have heard back from one team so far. Here is what they said: First I would suspect the soil to be silt masquerading as clay. Volcanos and clay don't usually go together. But Australia is a much older land mass than I've ever seen. We've had some issues mixing lime with clay, where it left the plaster soft, crumbly. Our theory is a large amount of clay to lime interferes with the re-carbonization of the lime. I've heard this doesn't happen with all clays, maybe some have available pozzolans, but we've never seen it. One could try a high amount of lime with a small amount of soil just for the color. We would keep them separate if tests reveal no benefit to mixing them, earthen base, lime topcoats. This information was submitted by Shahoma and Prasad Boudreaux, natural builders, natural plasterers, and educators at http://www.mixingitup.us/index.htm . Q: Due to several restricting factors in our house design, 2 of our walls will be left with no over-hang of the roof to protect them from the fierce sun and monsoon rains. We therefore need an enduring and hardy plaster for these walls. Everyone is telling us that cement is the best/only option and although the walls are small and would therefore not require huge quantities, we would like to find another option. Can lime plaster be any better than cement when considering the effects on the ecology? A: (Kelly) Cement manufacture is a major contributor to greenhouse gas accumulation whereas the manufacture and use of lime plaster has an eventual net neutrality in this issue, since the CO2 that is released during its manufacture is then reabsorbed as the lime cures. While lime is not as hard and perhaps as durable as cement stucco, it still lasts a long time and is easy to repair. Q: Both American Clay and Bioshield claim that their clay plasters work great in bathrooms. Are you familiar with those products/companies? Do you have personal experience with clay plaster in a bathroom? A:
I have experience with American Clay plaster and Bioshield products. I also have experience installing my own home-made clay paints (Alis etc.,) and clay plasters in bathrooms. Although clay plasters can perform well in bathrooms, the conditions need to be extremely supportive of the materials. A dry, well ventilated bathroom with no previous mould or moisture problems may be fine for this kind of installation. Q: Our bale house in upstate NY is nearing livability and we are working hard to finish the inside. We will use lime plaster over earth on the outside and I had intended to do so on the inside too, but, during the building of our interior (dry wall) walls, there have been buckets of that lovely white joint compound around and I could not resist troweling it on to a remote spot over an earth plastered bale wall. I wet the earth plaster and the first coat of joint compound went on like the crumb layer over a hard brownie, not nicely at all, like a lovely thick mud - and full of brown blotches when dry. Having begun though, I decided to stick it out and the second layer looks very nice. It was also nice not to have to run the cement mixer, scooping the clean, white plaster, pre-made, out of a bucket (our house is too big and we are tired). It will be winter here until mid May and I didn't want to get into the lime plaster until it was warm - AND I have to travel 8 hrs to the limeworks in Pennsylvania to get the lime plaster I want (no, I am not making it from scratch, though I did make mountains of earth plaster from my back yard...) Anyway, I liked the joint compound wall so well, I'm thinking of doing the upstairs bedroom walls in it - this will ease the spring lime plastering push as I can get this stuff locally and be working on it now without factoring in weather (our house is heated now but I think lime is too messy and too permanent to be mixing in the living room). If this works, I'm left wondering why, except in the bathrooms, I would use lime inside. So, here are my three questions: 1. The wall I did seems fine and looks nice, but is joint compound really ok to use over straw/earth plaster? 2. If this joint compound is going to be the finish plaster for the bedrooms, I obviously can't seal it with the usual latex paint, so I am thinking an alis or milk paint. It looks like clay plasters need to be primed if being applied over joint compound, so I'd assume application of an alis would also require that. I'm looking for short cuts, so if I can just mix up a milk paint to seal (and color) the joint compound, both on the bale walls and on the adjoining drywall walls, I'd happily go that route. Do you see any adhesive or other drawbacks to using milk paint on the joint compound over earth plaster over straw? 2. Joint compound comes premixed in those wonderful buckets BUT, I don't want a hundred of those buckets around. I've noticed that I can buy dry joint compound in bags, but I've only seen the dry in "fast setting" types. These cure chemically - sort of like lime. These also claim less shrinkage and cracking, both attractive qualities and I can mix them up by hand, as thickly as I want and as needed. Do you see any problem with using this fast setting compound over the earth plaster instead of the "drying" type compound that comes in the bucket? Also, I think this stuff (as contracted with the stuff in the buckets) dries to a light gray, will a white/light milk paint cover that? A:
No you do not have to plaster the interior of your straw bale with lime plaster. It is a good idea to use this in the bathrooms though. If you are simply after a white or light coloured plaster, you can make an earthen plaster using white clay, purchased from ceramic stores (pre-processed, no more sifting for you!). You may also use a Gypsum plaster for a light reflective surface, but then you are at the mercy of a chemical 'set time' for the gypsum plaster depending upon which type you have access to. Nontoxic Alternatives There are nontoxic alternatives to the conventional highly toxic joint compounds. One such brand is called Merco. It has natural binders and has no fungicides or preservatives. Dry wall experts say using this type of joint compound is a little more difficult but the quality and finish of it is far superior. Merco comes as a powder and has to be mixed fresh on the construction site and used that day so it's a little more labor intensive. Up to 4 layers, instead of 2 or 3, may be required. After sanding it, however, the drywallers -- whose first experience with it was in our new home -- said it finished like glass. For the homeowner they reported only advantages, saying it bonded to corners better than conventional joint compound, looked better, and was stronger. They stated the quality of the non-toxic alternative was so high it would never crack. The drywall mud I am familiar with is spelled "Murco", this may be the same one in the article above. Murco's taping compound is named M100. Here are the details if you want to use something else when mudding, taping and texturing your sheetrock walls. I realize you are tired of digging and mixing a lot of mud. One thing I can offer you, is that you will not have to mix nearly as much plaster for your top coat. If your base coat of earthen plaster is done well (smooth and shaped to your liking) you can float 1/4" of a white (or whatever colour, yellow, green...) earthen plaster on top. It is easy to mix, you might be able to do it in smaller batches with a drill (depending upon the size of your house). Either way, you will not have to have the mortar mixer running all day. In addition, you can apply this on top of your sheetrock walls as well. You can also apply Alis directly to new sheetrock.Milk paint is a little more complex to use. I do not know how it responds when applied to joint compound. The most important thing to know is that whatever the subsurface, it needs to be stable, clean and dust free. Milk paints have a surface tension when curing and can peel if the subsurface is not secure. Funny about those buckets, most of us in this business can never find enough of them! Q: For a project in Africa I've designed some dome structures. But due to the high cost of cement and transportation to the building side, I must find an alternative interior plaster. For the outside we will use cow dung. The natural resources are: salt, volcanic rock, volcanic sand. I wonder if it is possible to make a plaster out of salt? A:
No, I do not know of any plasters made with salt. Usually we are trying to remove the salts to prevent a condition known as "efflorescence". I would look to the locals to find out what kind of plaster they typically use in the region you are working. The most common plaster is made from mud, a local prolific resource in most places. The Basotho women of South Africa are known for their Litema designs. There is a research paper named 'The Revival of Litema: New Hope for a Disappearing Art' by Ms Carina Mylene Beyer. It might be a good resource for you if you are interested in more information. C: Mud is not available in the right structure. Due to the salt lake and the relative 'new' volcanic landscape there are no natural binding materials other than dung. But I've seen people gather the salt and building small towers out of the dried salt. Of course when it rains the salt will crumble. The locals only use dung for their houses, but they're constructed much different than the domes I've designed. I need also an interior plaster, and was hoping for the natural white colour of the salt. And because it is supposed to be for interior use only I found it probable that moisture absorption would be very limited. But I couldn't find any lead to a salt plaster of any kind. Perhaps it's possible to use it as a thin layer on top of the dung mixture. I will experiment and perhaps I will find a sustainable way of using the salt. Q: I am trying to develop a project with children to run in inner city schools in the UK. Most schools have no garden space so I have been experimenting with ideas from Kiko Denzer in earthen plaster murals. I am experimenting with earthen plaster onto an outdoor brick wall and also waterproofed ply tiles (about 30cm square). Once applied, I sculpt into it. I want to paint the surface with bright coloured natural pigments and then to seal these in. I have used waterglass mixed with water 50/50 but the earthen plaster and painted pigments still seems to wash away after about 3 months, exposing the earthen plaster again. I have seen that I could try linseed and people have mentioned casein, borax, lime plaster, clay alis etc. As the murals will potentially be on exposed walls what do you think would be the best preserver of the pigments whilst also stopping the mud washing away? A: It sounds like you are doing a wonderful project. Sorry to hear the murals are washing away. There are many details to consider in regard to the success of mud murals in exterior settings: site, design, detailing, and of course materials. If I were in your position, I would run a number of test panels and expose them to the elements in the same location. You can also simulate rain using a garden hose to test durability in regard to water penetration and erosion. Make sure your samples are mimicking their final resting place. For example, stand sample up vertically (as if it were on a wall) as opposed to laying them flat where water could pool on them. You will have to take special care to seal the edges if you are testing individual boards. A mural is quite different, and has less areas for water to infiltrate. You have been using Waterglass currently. Are you using Sodium Silicate or Potassium Silicate? Although I have never worked with Potassium Silicate, I understand it is much more durable than the Sodium Silicate. If you are working with these you want to be using Silica sand in your mix to increase the bonding actions of the materials. I would make some test panels using Linseed oil (or other oils). That is an easy one to work with. By the sounds of what you may be dealing with weather-wise, I would not look toward borax or lime casein, nor would Alis work for your situation. Alis would be an excellent way to apply the colour for the decorative elements of the murals, but then I would look for something super durable for the protection you are needing. In regard to the Linseed oil tests. If you warm the oil up it can penetrate into the plaster more deeply. Try multiple coats (you may have to dilute them as you, depending upon how porous the plaster is). Then try another sample with multiple coats of oil and finish it off with Beeswax, just the same as an adobe floor. Lime plaster may work as it would definitely prevent water erosion (you may want to use hydraulic lime). However, lime is more tricky to work with (and can be a skin irritant due to it's high alkalinity), particularly if you are working with young people. Their age may determine the appropriateness and success of this option. Lime would also limit the colour range you would be able to work with. You could look toward waxes, and even wax in conjunction with the linseed oil. For more details on these types of applications you may want to consult Adam Weismann and Katy Bryce's book "Using Natural Finishes". They have a resource list that is on-line. I have also clipped out a couple of resources that may assist for materials or products to use in weather protection. www.naturalpaintsonline.co.uk The last option may be to look toward 'product' for sealing options. Keim paints makes ecologically friendly paints and sealers. Consult their product listing to see if anything may be compatible with your project. Some 'products' you may be able to add as an integral ingredient to the mix. Some of us are using Soy Resin here in the US. You can add this directly into the mix to prevent erosion (instead of just painting it on top). Depending upon what products you may find there, you may have either option. Q: We have a timberframe/strawbale home in Bozeman, Montana. The house was completed a few years ago and has more than a few dings in the wall, from furniture moving and our children. Also, the finish is quite rough and I am interested in smoothing out the plaster finish, and changing the color. We have a great local sustainable building store here in Bozeman, called Refuge Building Supplies. They carry a product called American Clay, which is used to put a natural clay finish on walls. I have picked out a pigment from that company (which comes separately from the clay bag) and want to know if there is a cheaper way to do it myself. I am confused about what type of clay to get, the type of binder (wheat paste?) if I indeed need a binder, and a good recipe for earth plaster. I am also wondering if I have to wet the walls first. We have fixed some deep cracks with silicone and joint compound...I am not sure if that was the right thing to do, but the builder recommended it. Do you have any ideas? A: Yes, there are cheaper ways to re-finish your walls than buying a product such as American Clay. You can make your own mix that will resemble American Clay's Loma finish. If you are interested in learning about this, I can point you in the direction of a book, or I can personally consult with you and walk you through the process, addressing your concerns in regard to cracks etc. Q: I have had a tough time finding information on applying a lime plaster to an existing interior wall that is already coated with latex paint. I am looking to refinish several walls in my home with a lime plaster, primarily for it's aesthetics, but also as an experiment and practice for future construction projects I hope to do. Do I need to prep the wall in any special manner before applying the plaster? I am planning on just using one coat of a pigmented lime plaster rather than multiple coats and a limewash. Will the lime stay on the wall and key into the paint? Does it matter if it keys into the paint once the plaster has hardened and become a continuous self-supporting entity? I am open to using an earth plaster with a limewash over it but have the same questions regarding the earth's ability to stick to the walls. Every other plastering job I've done has had lath or a rough, uneven surface for the plaster to key into. A:
Attaching lime plaster to any surface and having long lasting enduring results can be difficult. Lime plaster is a fine art that requires much more knowledge that earthen plasters for success. I do not know of anyone who has had success attaching lime directly to a smooth surface without some sort of armature. This could vary depending upon the type of the product (of lime), the thickness, and the wall itself. Any applications I have done have been over expanded metal lathe that was secured to the wall in advance. |
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Janine Bjornson is a natural builder, practitioner and educator. She began her career in natural building when she trained with The Cob Cottage in 1996. Since then, she has taught over 50 workshops in Canada and the United States, from east to west. Her passion for building with natural materials bloomed out of her love for the earth, in conjunction with her concern for diminishing ecological resources and toxic buildings. As a result of this, Janine has devoted the last decade to immersing herself in the world of natural materials and the knowledge of how we can shape dwellings that are healthy, healing, inspiring, and beautiful. She has developed a penchant for natural paints, and plasters and loves the concept of “naturalizing” any kind of home. She loves to share this knowledge with others and this is evident in her enthusiastic teaching style. Janine has assisted in organizing 2 Natural Building Colloquia and she has presented at 3 of them. She teaches the natural building component of New College of California's EcoDwelling program. She lives in Sebastopol, California.
